Add support to MDX in blog

src/utils/frontmatter.js

@@ -0,0 +1,11 @@
+import getReadingTime from 'reading-time';
+import { toString } from 'mdast-util-to-string';
+
+export function remarkReadingTime() {
+  return function (tree, { data }) {
+    const text = toString(tree);
+    const readingTime = Math.ceil(getReadingTime(text).minutes);
+
+    data.astro.frontmatter.readingTime = readingTime;
+  };
+}